1. Technical Field
The present invention relates to a fluorescent labeling reagent for a biological label to detect a biological material in medical and biological fields or the like.
2. Related Arts
In recent years, developments have been made on various measurement methods and materials for optically detecting a biomolecule, using a fluorescent labeling compound in which a material capable of being adsorbed on or bound to a specific biomolecule contains a fluorescent material. The measurement using such a fluorescent labeling compound includes, for example, DNA chip for detecting a specific DNA sequence and a detection of antigenic material using antibody. The measurement using the fluorescent labeling compound is also applicable to Flow Cytometry which detects the specific material or biological cell having the specific material. Further, the fluorescent labeling compounds are used in Bio-imaging to visualize by fluorescence where the specific materials exist in biological body, by directly dispersing the fluorescent labeling compounds into the biological body.
These use the phenomenon that, when the fluorescent labeling compound which has been adsorbed on or bound to the biomolecule is exposed to light, the fluorescent material absorbs the light so as to emit light at a specific wavelength. For the fluorescent material contained in the fluorescent labeling compounds, the organic dye, metal complex, semiconductor nanoparticle, and the like are generally used.
For example, U.S. Pat. No. 5,990,479 discloses Group II-VI semiconductor nanocrystals for biological probes as visible luminescent inorganic particles. These emit light in visible region by using short-wavelength UV light or visible light such as blue light, and the like as an excitation light source.
Further, JP 2003-525282 (a published Japanese translation of PCT application) discloses fluorescent quinoline ligands as a fluorescent material emitting in the near-infrared region (NIR). This publication describes fluorescent organometallic complexes.
Fluorescent probes emitting in visible region have been mainly used as fluorescent probes to examine the biomedical tissues. This reason is the conveniences such that it is possible to directly confirm the luminescence state with the naked eyes and that the images can be recorded with various existing imaging devices. However, it is required to use the excitation light source which has a wavelength shorter than the fluorescence wavelength of the fluorescent material, and therefore, there is a problem that the excitation light source having such a shorter wavelength, especially a laser source, is expensive.
Further, in the case of using a xenon lamp or LED, since its spectrum is broad, a component of the fluorescence wavelength regions of the spectrum must be cut by using a proper diffraction grating or light filter, thereby causing the complication of the measurement system and the decrease in excitation light intensity.
Furthermore, in the case of using ultraviolet ray as excitation light, higher intensity of the light may cause destruction of the biomedical tissues such as cells. In addition, since many of the biomedical tissues derived from higher organisms such as mammal contain a dye which easily absorbs the visible light, there is also the problem that the excited light cannot penetrate into the specimen or that the radiated fluorescent cannot be taken out from the specimen.
On the other hand, there is a fluorescent material for biological label containing an organic molecule or an organometallic complex which absorbs the near-infrared light and then radiates the near-infrared light. However, the fluorescent material containing the organic molecule is gradually destroyed due to the repetition of the interaction with light, thereby causing the problem of the color fading that the fluorescence intensity decreases gradually while measuring it for a long time.
Further, the fluorescent labeling compound using the organic dye has problems of an unstable fluorescence wavelength and a short life. The fluorescent labeling compound using the organometallic complex has a problem that the fluorescence wavelength and intensity are liable to variation due to the ligands and the like. As a material capable of solving the problems of the instabilities, use of semiconductor nanoparticle for the fluorescent material has been examined. However, control of the particle size of the nanoparticle is not easy, resulting in occurrence a problem that the fluorescence wavelength varies depending on the particle size of the semiconductor nanoparticle, and therefore, the detected fluorescent intensity varies. In addition, in order to control nonradiative trap level formed on the surface of the semiconductor nanoparticle and cause the semiconductor nanoparticle to emit light efficiently, a particle having a structure called a core shell structure in which the semiconductor nanoparticle is coated with other semiconductors etc. has been generally manufactured. However, this increases the manufacturing cost. Moreover, there is a problem that the semiconductor nanopaticle made of cadmium or selenium has toxicity.